Being a heavy stoner through 25 is highly correlated with at least alcohol consumption, pre-existing mental health problems, and polysubstance abuse.

That said intuitively that weed makes you stupid and crazy doesn't surprise me in the slightest. Unfortunately smoking weed is the most fun before things get serious with work and family in late 20s.

Another thing that came to mind, in the creativity enhanced altered state I'm currently in and have been in since age 12, is the exact mechanism is still up for debate regardless of established causality. I'm hoping the IQ decline comes from sitting stoned playing video games over engagement in school and work, as opposed to THC itself directly causing neurological learning deficits that are not reversible

I don't remember the 'smartest' people turning up to school with cans of energy drink, going to parties, being obese, smoking every day and bragging about it, so that has always been my conclusion. I don't consider myself one of the smart ones, before anyone downvotes, I've had my own issues with addictive/compulsive behaviors which certainly took a toll on my academic & social performance in HS.